#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	int a[] = { 1,2,3,4,5,1,2,3,4 };
	int sz = sizeof(a)/sizeof(a[0]);
	int ret = 0;
	for (int i = 0; i < sz; i++)
	{
		ret ^= a[i];
	}
	printf("%d\n", ret);
	return 0;
}